A variety of compounds having activity for lowering parathyroid hormone levels have been described. See International Publication No. WO 2011/014707. In one embodiment, the compound may be represented as follows:

The main chain has 7 amino acids, all in the D-configuration and the side-chain cysteine residue is in the L-configuration. The amino terminal is acetylated and the carboxyl-terminal is amidated. This compound (“AMG-416”) has utility for the treatment of secondary hyperparathyroidism (SHPT) in hemodialysis patients. A liquid formulation comprising AMG-416 may be administered to a subject intravenously. The hydrochloride salt of AMG-416 may be represented as follows:

Therapeutic peptides pose a number of challenges with respect to their formulation. Peptides in general, and particularly those that contain a disulfide bond, typically have only moderate or poor stability in aqueous solution. Peptides are prone to amide bond hydrolysis at both high and low pH. Disulfide bonds can be unstable even under quite mild conditions (close to neutral pH). In addition, disulfide containing peptides that are not cyclic are particularly prone to dimer formation. Accordingly, therapeutic peptides are often provided in lyophilized form, as a dry powder or cake, for later reconstitution. A lyophilized formulation of a therapeutic peptide has the advantage of providing stability for long periods of time, but is less convenient to use as it requires the addition of one or more diluents and there is the potential risk for errors due to the use of an improper type or amount of diluent, as well as risk of contamination. In addition, the lyophilization process is time consuming and costly.
Accordingly, there is a need for an aqueous liquid formulation comprising a peptide agonist of the calcium sensing receptor, such as AMG 416. It would be desirable for the liquid formulation to remain stable over a relevant period of time under suitable storage conditions and to be suitable for administration by intravenous or other parenteral routes.